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In the muscle-wasting genetic disorder Duchenne muscular dystrophy, muscle is replaced by scar tissue. This leads to progressively weaker skeletal muscles and paralysis, breathing and heart problems, and eventually, death. Current drugs can improve symptoms but not change the course of the disease.

Mice with a form of the disease were given oral tamoxifen from 3 weeks of age for more than a year, at lower doses than used in breast cancer. They had improvements in their leg muscle strength and stamina, half the amount of scar tissue in their hearts, and less scar tissue and more muscle in their diaphragms. Their whole body strength was close to that of normal mice after a year, making them able to cling onto a wire. The results were published in the American Journal of Pathology.

Mouse muscle affected by the dystrophy has higher than normal levels of estrogen receptors and higher plasma creatine kinase activity. Tamoxifen normalizes the increased levels of the enzyme, and this could be through an estrogen receptor (ER) dependent mechanism.